EFFECT OF TURNING AND BRAKING ON THE POLISHING OF ROADSTONE BY TRAFFIC

This report describes a study that has been made of the extra polishing of aggregates in bituminous surfacings that takes place at sites where traffic is turning or braking. The sites studied included bends with radii varying from 40 metres to 250 metres, approaches to road junctions and approaches to pedestrian crossings. A detailed study was also made of the distribution of different levels of resistance to skidding at a roundabout. It is concluded that aggregates to be used in surfacing at most sites where traffic is turning or braking should have a psv at least 5 units higher than that which is indicated for similarly trafficked event-free sites, in order to maintain the same level of resistance to skidding. Approaches to pedestrian crossings (unless they are near junctions or are on bends) do not appear to need so high a psv (only about 1 unit above that indicated for an event-free site). It is emphasized that these increases in psv are to maintain the same level of resistance to skidding as at similar event-free sites, and do not take into account any possible need for a higher level of resistance to skidding due to the greater risk of accidents. /Author/TRRL/